Neurons containing latency-associated transcripts are numerous and widespread in dorsal root ganglia following footpad inoculation of mice with herpes simplex virus type 1 mutant in1814

Abstract

The herpes simplex virus type 1 (HSV-1) mutant in1814 lacks the ability to trans-activate immediate early gene transcription and enter lytic replication but it can establish and reactivate from latency. We therefore investigated the number of neurons that expressed latency-associated transcripts (LATs) in animals latently infected with in1814, the rescued revertant (1814R), or wild-type (wt) HSV-1. The percentage of LAT + neurons increased with increasing doses of each of the viruses. After inoculation of equal amounts of infectious virus many more LAT + neurons were observed in animals infected with in1814 than with 1814R or wt HSV-1.Whereas the LAT + neurons in animals infected with 1814R or wt HSV-1 were largely confined to lumbar dorsal root ganglia (DRG) L4/L5/L6 (those which innervate the lower leg), in animals infected with in1814 they were also present in DRG not directly involved with such innervation (thoracic 12 and 13, L1, L2 and L3).We concluded that the large number of LAT + neurons observed with in1814 was related to the high particle numbers in the inoculum and that spread of virus was related to limited replication as well as to the low neurovirulence of in1814. This spread was not unique to in1814 but when it occurred with more virulent viruses such as 1814R or wt HSV-1, it resulted in the death of the host.

Long-Term Transgene Expression in Mice Infected with a Herpes Simplex Virus Type 1 Mutant Severely Impaired for Immediate-Early Gene Expression

“…To a first approximation, in1388 established latency in the DRG with an efficiency comparable to that of a VP16 mutant (in1851), which is unable to replicate in neurons due to an insertion that disrupts the TK coding sequences (12), since the number of ␤-galactosidase-positive neurons after inoculation with in1388 is similar to the number of LAT-containing cells in in1851-infected mice when the same routes of inoculation and approximately equal titers of virus are used. Between 1 and 2% of DRG neurons (based on a value of 10,000 neurons in L3, L4, and L5 DRG [12]) expressed ␤-galactosidase by 25 days postinoculation, although this value underestimates the proportion of positive neurons in the infected population.…”

“…Between 1 and 2% of DRG neurons (based on a value of 10,000 neurons in L3, L4, and L5 DRG [12]) expressed ␤-galactosidase by 25 days postinoculation, although this value underestimates the proportion of positive neurons in the infected population. Many DRG neurons project to parts of the limb other than the foot, and even within the foot not all nerve endings would be exposed to the inoculum.…”

“…ICP4 is not required for latency or production of LATs, since viral DNA and neurons containing LATs can be detected after infection with viral ICP4 deletion mutants (11,26,49). It was found that mutant in1814, defective for VP16 function, established latency in mice apparently as efficiently as wild-type HSV-1 when comparisons were made on the basis of PFU in the inoculum, demonstrating that functional VP16 is not absolutely required for latency (12,53). Similarly, viral mutants lacking functional ICP0 were able to establish latency and to reactivate, although they were attenuated for replication in mice (4,7,31).…”

An analysis of herpes simplex virus gene expression during latency establishment and reactivation.

“…Such viruses are unable to initiate lytic cycle infection in non-complementing cells in culture (Ace et al, 1989 ;DeLuca et al, 1985 ;Jamieson et al, 1995 ;Preston et al, 1997 ;Wu et al, 1996). However, a number of such mutants can efficiently establish latent infection in neurones in vivo (Chiocca et al, 1990 ;Ecob-Prince et al, 1993 ;Sedarati et al, 1993). These data suggest that latency can be established in the absence of any lytic cycle gene expression, and may therefore represent a ' default ' pathway which occurs following virus entry into a cell that is non-permissive for the initiation of lytic cycle gene expression.…”

Expression of beta-galactosidase in neurons of dorsal root ganglia which are latently infected with herpes simplex virus type 1

“…Serial sections of the embedded DRG from all the mice involved were then investigated by ISH for the presence of LATs or fl-galactosidase mRNA. The ISH technique was carried out using 35S-labelled riboprobes as described previously (Ecob-Prince et al, 1993a).…”